Specimens from thirty-four knees in twenty-eight patients with
histologically proved osteonecrosis were reviewed. Twelve knees had the
clinical diagnosis of so-called idiopathic osteonecrosis; eight,
osteoarthrosis; and fourteen, rheumatoid arthritis. Pathologically, the
necrosis was localized in the subchondral region of the medial femoral
condyle in 67 per cent of the knees. There were pathological fracture and
collapse and fragmentation of the necrotic segment leading to marked
deformities in most cases. The response to necrosis consisted of
histiocytic resorption of necrotic material and formation of granulation
tissue and reactive new bone surrounding it. The response was relatively
less prominent in the knees with degenerative joint disease and rheumatoid
arthritis.